The Two Major Anatomical Areas of the URT which are prone to ‘Performance Limiting’ Dysfunction are the LARYNX and PHARYNX.
LARYNGEAL DYSFUNCTION Dysfunctions of the larynx include:-i) left or right laryngeal paresis or paralysis ii) left and / or right dilation and prolapse of the lateral ventricles and associated vocal folds. iii) 4BAD-fourth branchial arch defects iv) arytenoid chondritis
PHARYNGEAL DYSFUNCTION
Dysfunctions of the pharynx include:-(firstly the most common) i) disruption of the ‘oropharyngeal seal’ (OPS) ii) disruption of the OPS with resultant DDSP iii) epiglottic entrapment (a) permanent (b) intermittent and occasionally observed during standing endoscopy (c) intermittent and only observed during treadmill endoscopy iv) pharyngeal dynamic collapse; dorsal,ventral and / or lateral wall collapse v) aryepiglottic fold vibration with dynamic collapse vi) epiglottic vibration and / or retroversion
Causes of dysfunctions, of the larynx and pharynx are numerous and a current count has revealed over 50 documented abnormalities which can contribute to this dysfunction. The etiology and pathogenisis of many of these conditions however are still the subject of much debate.
Incidence of dysfunctions. Most current treadmill studies rate Pharyngeal dysfunctions i)* and ii) as the most common ahead of combinations of Laryngeal dysfunctions i) and ii).
* This dysfunction is often observed but not often directly referred to as such!
PHARYNGEAL FUNCTION
(A) Normal; put simply, the pharynx acts to direct food and water into the alimentary tract and air into the respiratory tract. Whilst eating or exercising, food / saliva and water should not enter the respiratory tract and air should not be drawn into the alimentary tract (oesophagus). Whilst exercising air should not enter or be drawn through the oropharynx into the respiratory tract. The consequences of this will be explained later.
This system of obligate nasal breathing and an inability to vomit have evolved to assist the horse in its major survival mode ‘flight i.e. it needs to be able to ‘eat and run’. During flight, some feed can be retained in the buccal cavity, whilst the bolus in the oropharynx is swallowed without contaminating the respiratory tract.Thus the horse can eat, run and evade its predator,without “choking’ -if swift enough!
i)DDSP is a normal and necessary part of deglutination as is the horses ability to selectively create and ii)disrupt the oropharyngeal seal (OPS) during swallowing. iii)Dorsal and ventral nasopharyngeal collapse are also a normal part of the protective and directive (directing food and water to the oesophagus) mechanism required for deglutination.
(B) Abnormal; if any of i), ii) or iii) (above) occur during exercise - if they do two further abnormal situations can result.
1) A reduction in the cross sectional area of a section or sections of the nasopharynx resulting in a reduction of air supply to the lower airways.
2) In the case of i) and ii) in particular contamination of the trachea and upper airways with oral contaminates which could eventually lead to ‘lower airways disease’. Oral contaminates found in tracheal washes.
ii)Disruption of the oropharyngeal seal (OPS) This seal is the primary mechanism by which the soft palate is maintained in a ventral position and the oral cavity is sealed off from the airway during exercise .
If the tongue is flattened and pushed slightly forward, which normally requires the incisors being slightly to at times maximally separated (usually if horse is pulling), air can enter the oropharynx from the buccal cavity. The rostral and mid soft palate now rise into the nasopharyngeal airway reducing its patency. With resultant increasing -ve pressures in the airway during inspiration, some air may eventually be drawn around the caudal free edge of the soft palate from the oropharynx. This air carries with it material which is then referred to as ‘oral contaminates’.
This whole process can be easily appreciated if one performs endoscopy whilst at the same time occluding the nostrils. Now have someone observe the occurrences within the mouth at the same time. It may be necessary to fit a gag to better observe these movements.
Endoscopically including during treadmill endoscopy it is not difficult to appreciate whether the OPS is patent or disrupted. If ‘patent’ there will be a deep trough in the caudo-ventral nasopharynx below the epiglottis, formed by the caudal soft palate adhering tightly to the glosoepiglottic mucosas and piriform recesses. The apex of the epiglottis sits above and in the main does not contact the dorsal surface of the soft palate. If ‘disrupted’ the caudal trough is not apparent and the caudal SP has a rounded appearance to it. Elevation of the mid and rostral regions of the soft palate is also apparent. The apex of the epiglottis now lies in contact with the dorsal surface of the soft palate which has risen to meet it.
It is at this point that the secondary mechanism for maintenance of ventral positioning of the soft palate comes into play. Both the base and apex of the Epiglottis are now the major players. Thus at this point epiglottic integrity and the presence or absence of epiglottic entrapments of any type become significant contributors to pharyngeal function.
i) DDSP : can only occur once the OPS has been disrupted. DDSP only occurs if the epiglottis is then unable to support the soft palate or if the horse consciously disrupts this hinge. If DDSP occurs during exercise both a reduction of air supply, and tracheal contamination result.
DIAGNOSIS ......OF PHARYNGEAL DYSFUNCTION ...by utilising ‘different combinations’ of the following forms of assessment,
1) Abnormal Noises with... i) Disrupted OPS- may be none-or more often a slight increase in both inspiratory and expiratory noise due to vibration of the soft palate (often described by riders as “slightly thick in the wind”).Structures about the intra pharyngeal ostium (aryepiglottic folds. epiglottis and caudal border of the soft palate) can be affected as orally inspired air is ‘ill directed’ and thus can create abnormal turbulence and vibrations (noises). These can often be duplicated using endoscopy whilst occluding the nostrils. It is often useful if the rider is present to compare these sounds to those which he / she has been hearing.
ii) DDSP, a loud biphasic intermittent or persistent stertor or ‘gurgle’ in approximately 50% of cases. Approximately 50% make no abnormal noise.NB. ... grunting, coughing (throat), gasping , breath holding (RRE) , swallowing and irregular breathing patterns are also often linked to pharyngeal dysfunction.
2) Endoscopy - to confirm using endoscopy the horse must be exercising on a ‘high speed treadmill’. However it is also important to realise that not all horses that dysfunction during a race or event will dysfunction during treadmilling. NB Standing endoscopy is really only of use as an elimination process. e.g....... “laryngeal function appears to be within acceptable limits.”..... “Gross EIPH is not apparent.”.......etc.
3) Tracheal wash - ‘significant contamination’ of the wash with oropharyngeal materials means .the pharynx is not functioning normally...... and therefore ‘pharyngeal dysfunction’ exists!! NB if tracheal contamination has been occurring for a considerable period of time then ‘lower airways disease’ may have resulted which together with increased inspiratory -ve pressures could then contribute to an increased level of EIPH.
4) Poor Performance- Stopping ,quitting, failing to run on, reluctant to ‘try’,.............in the absence of other significant factors.....e.g......lameness, cardiac arrhythmias., acute EIPH..............etc.
5) increased post race recovery times....Resp.rate....heart rate. NB; some horses with a history of these dysfunctions appear ‘not to try’ and thus do not experience respiratory embarrassment , and will recover ‘normally’.
6)Abnormal behaviour- race, event (cross-country) or training associated reluctant, hyperactive and / or nervous behaviour. The 100’s of cases where this behaviour was permanently altered following successful surgical treatment of upper respiratory tract problems, has confirmed this link in many individual cases.
7) Reduced appetite- when racing and in heavy training- most probably secondary to airway contamination and exercise induced LRT inflammation ..hyper responsiveness...etc
IMPORTANT...Upper and Lower airways abnormalities often co-exist.
